This invention relates to optical analyzing instruments, and, more particularly, to optical analyzing instruments for testing samples from the reflective or transmissive optical densities of the samples.
The optical density of a sample refers to a transmissive or reflective characteristic of the sample. Transmissive optical density is defined as the logarithm of the ratio of the intensity of incident light on the sample to the intensity of light transmitted through the sample. Reflective optical density is defined as the logarithm of the ratio intensity of the incident light on a sample to the intensity of the reflected light from the sample. U.S. Pat. No. 3,861,788 issued to Donald R. Webster on June 21, 1975, discloses an instrument for analyzing test samples by detecting differences in optical density at selected wavelengths. The specific application for which this instrument is designed is to measure oil, water and protein content in grain samples. In the instrument of the patent, interference filters are mounted in a paddlewheel configuration, which rotates the filters in sequence into a light path between a source of light and the test sample to be analyzed. The paddlewheel arrangement not only moves the filters in sequence into the light path, but also varies the angle of incidence of the filter to the light as the filter moves through the light path. As the angle of incidence of the light to the filter varies, the wavelength of the light transmitted through the filter varies. Thus, as each of the filters passes through the light path, the wavelength of light incident on the test sample sweeps through a range of values. The instrument detects the intensity of the reflected or transmitted light at specific selected positions of the paddlewheel to measure differences in the optical density of the test sample. This technique of measuring the constituents of test samples has proved to be very accurate.